1. Field of the Invention
The present invention relates generally to a short-range mobile communication system, and more particularly, the present invention relates to a slave apparatus of a short-range mobile communication system operating in within a walking distance for receiving data stored in a master apparatus through a given radio link, and a method for receiving data.
2. Description of the Related Art
A short-range mobile communication system is an apparatus and means for transmitting or receiving message data and voice data in real time between electrical products usually located within a diameter of 10 meters from each other, such as a cellular phone, notebook computer, desk top device and so on. The short-range mobile communication system usually consists of a master device transmitting data and a plurality of slave devices receiving data. However, the master would be considered a slave if it only receives data. That is, the function of a master or a slave is not fixed.
The most well known short-range mobile communication systems is a method known as Bluetooth™, that has been suggested by Ericsson and Nokia. The Bluetooth™ application allows various electrical products, such as a mobile terminal, notebook computer, facsimile and MP3 player, to be accessed by each other through a radio link. The detailed transmission standard that has been suggested by Bluetooth™ has an advantage to make products highly protected from interference and provides security of data. Radio communication means using the Bluetooth™ application could be manufactured very small, like a microchip, that is easily attached or incorporated into electrical products. Furthermore, radio communication means using the Bluetooth™applications are designed to use the frequency band of 2.4 GHz, and are capable of communicating all over the world. The Bluetooth™ standard designates two power levels. At low powers levels it is designed to operate within a room, while at high power levels, it is designed to operate within the whole house.
The Bluetooth™ radio technology is designed to work on both point-to-point access and point-to-multipoint access. According to the Bluetooth™ standard, a master can concurrently communicate with a maximum of seven slaves. However, communication between a mobile phone and a headset using conventional Bluetooth™radio technology is usually implemented through a Synchronous Connection Oriented (hereinafter SCO) link that is usually a full duplex link and point-to-point access for voice communication. Referring to FIG. 1, the master 1 and the slave 2 comprise a short-range mobile communication system. Namely, the master 1 consists of the main part 3 and a short-range mobile system 4. The main part 3 includes a control unit 5 controlling the whole operation of the master 1 and memory 6 storing data, for example an MP3 file, received from computers or wire/wireless communication means. The short-range mobile system 4 attached to or incorporated into said main part 3 is the same or similar to the structure of other wireless systems. That is, the short-range mobile system 4 consists of a base band module 8 connected to the main part 3, a memory 9 for storing programs for controlling the operation of the baseband 8, transceiver 7 and antenna 10.
Meanwhile, the slave 2 also consists of a short-range mobile system 4′ that is the same or similar to the short-range mobile system 4 attached to or incorporated in the master 1, and a headset 11. The headset 11 consists of PCM decoder/encoder 12 for decoding data received from the short-range mobile system 4′, speaker/earphone 13 for transforming data provided by the PCM decoder/encoder 12 to audio data, and a mic 14 for transforming voice signal of a user to an electrical signal. Therefore, in order for the slave 2 to receive data from the master 1, an SCO radio link is usually established between them. The SCO link is designed to require the use of TDD (Time Division Duplex) and has no problem with a maximum 64 Kbps of transmission of voice and short message data. However, when the short-range mobile systems 4 and 4′ are linked by SCO radio link and a user wants to receive an MP3 file, the MP3 file can not be properly transmitted in time because of the large size of the file.
Now, to solve the above problems, an Asynchronous Connection-Less (hereinafter called ACL) link has been recommended as an alternative method for transmitting data quickly in a short-range mobile system. The ACL link is designed to use the method of packet switching, while the SCO link is designed to use the method of circuit switching. Therefore, the ACL link transmits data faster than the SCO link even in the same frequency band. If the main part 1 is designed to use both a low speed radio link and a high speed radio link, the master 1 selects only one pertinent radio link just before data transmission.
The method of data transmission using the ACL link for a high speed data transmission between the master 1 and slave 2, was disclosed in the Bluetooth™ standard and conference documents presented by Dr. Jaap Haartsen of Ericsson on Jul. 9, 1999 in Toyko, Japan. According to the standard and documents with respect to Bluetooth™, the control 5 of the master 1 determines what kind of data is transmitted; a low speed data-voice, short message data less than 30 letters, or a high speed data-MP3 file, picture file. After determining the kind of data, the baseband 8 of the master 1 of the short-range mobile system 4 establishes a selected radio link. However, although the ACL link and the method of multiple packet transmission was disclosed, no information is provided in the case of a large file, like an MP3 file, which is transmitted to a slave 2 through a short-range mobile system, and how the slave 2 selects the received data and outputs the data.